1. Field of the Invention
The invention concerns a device for redirecting beamed light while it is being transported through air in a hollow tubular light pipe or conduit. The invention is especially concerned with such devices that are designed to function as a luminaire.
2. Description of the Related Art
U.S. Pat No. 4,260,220 (Whitehead) reports three prior methods of directionally transporting beamed light through a hollow tubular light pipe or conduit:
"A first method, as exemplified by U.S. Pat. No. 3,506,331 which issued to R. Kompfner on Apr. 14, 1970, is to use focusing lenses or mirrors at intervals down a hollow pipe. In a second method, a hollow pipe with a mirrored inner surface is used to keep the light traveling down the pipe, such a pipe is shown in U.S. Pat. No. 3,700,900 which issued to G. A. Herleikson on Oct. 22, 1972. In a third method which is illustrated in U.S. Pat. No. 3,583,786 issued to E. A. G. Marcatili on June 8, 1971, the pipe consists of an inner cylinder, usually air, surrounded by pairs of dielectric layers wherein the losses are purported to decrease with the number of layers."
The Whitehead patent concerns a fourth method wherein the hollow tubular light pipe or conduit is a rectangular structure of transparent dielectric material having planar inner and outer surfaces which are in "octature," i.e. the outer planar surfaces form 90 degree angle corrugations, the faces of which extend at 45 degrees to the other surface. This hollow tubular light guide or conduit is said to provide "total internal reflection" (TIR). Because some of the beamed light inevitably leaks out through the transparent walls, Whitehead's device acts as a luminaire, even though nothing is said about it doing so.
A second Whitehead patent, U.S. Pat. No. 4,615,579, concerns modifying the structure of the first patent so that it releases the transported light in a controlled manner through one or more walls of the structure to enhance its utility as a luminaire. Even when so releasing light, the structure can be called a "hollow TIR conduit" because it incorporates principles of total internal reflection.
Coassigned U.S. Pat. No. 4,805,984 (Cobb) likewise directionally transports beamed light through a hollow TIR conduit that differs from those of the Whitehead patents in that the cross section of its wall lies in a smooth arcuate curve (preferably circular in cross section), and its structured surface consists of a linear array of substantially right-angled isosceles prisms arranged side by side. The perpendicular sides of each prism make angles of approximately 45 degrees with the tangent to the adjacent smooth surface opposite the structured surface. Imperfections in the wall member of the hollow TIR conduit of the Cobb patent allow some of the transported light to escape through the wall member so that the TIR conduit can act as a luminaire.
The TIR conduit of Cobb '984 can be made from the thin, flexible film disclosed in coassigned U.S. Pat. No. 4,906,070 (Cobb). Such a film is currently marketed as SCOTCH.TM. Optical Lighting Film No. 2300 acrylic (from 3M Co.) and reflects light rays at angles of incidence up to 27.3 degrees to its smooth surface. In a hollow TIR conduit of the N2300 acrylic lighting film, 50 percent of a beamed light can be transported a distance 60 times the diameter of the tube. When the hollow TIR conduit is to be used as a luminaire, the escape of light can be enhanced by adhering SCOTCH.TM. light extractor film V5115 to the inner face of the hollow TIR conduit in areas where light release is desired.
For use as a luminaire, a TIR conduit is mounted in a housing, and a lamp and paraboloidal reflector are mounted at one end of the housing. At the other end is either a second lamp or a mirror. The housing can be transparent in some areas and opaque in others, and the opaque areas can be covered by reflective material.
Because paraboloidal reflectors are usually called "parabolic reflectors," the latter term is used here. Parabolic reflectors are only substantially paraboloidal for reasons well known in the art.
In spite of the availability of hollow TIR conduits, almost all luminaires in current use are fluorescent lamps. For example, fascia signs are often lighted by strings of fluorescent lamps, but areas between adjacent lamps may be poorly lighted, and the failure of one lamp is highly conspicuous.
Luminaires based on known hollow TIR conduits involve the same problems, except that the length of a single hollow TIR conduit can be much greater than is feasible for a fluorescent lamp. Another advantage of a TIR luminaire versus fluorescent is that two lengths of a TIR conduit can be interconnected at an angle, and a mirror could be positioned at their juncture to redirect the light from one to the other. However, the areas of their wall members behind the mirror would be shielded from the light, thus leaving a dark area in the otherwise lighted luminaire.
While neon luminaires can be bent and exceedingly long, they are expensive and involve other shortcomings.
Other Prior Art
U.S. Pat. No. 4,557,565 (Ruck et al.) discloses a transparent panel consisting of a series of linear prism facets that is used to illuminate a room by deflecting sunlight, e.g., onto the ceiling. That type of transparent prismatic panel could be used as the light-redirecting prismatic element of a hollow tubular light conduit of the present invention to redirect light 90 degrees.